Improve docblock on HarkSurvey.cloneSurvey

Civi/Api4/Action/HarkSurvey/CloneSurvey.php

@@ -28,7 +28,11 @@ class CloneSurvey extends \Civi\Api4\Generic\AbstractAction {
   protected $newTitle;
 
   /**
-   * Depth of clone, one of: survey, participants, full
+   * Depth of clone, one of:
+   *
+   * - survey: just the definition
+   * - participants: the survey and the participants but not their answers
+   * - full: the survey, its participants and the answers.
    *
    * @var string
    * @default survey